The number 21021
21021 is a composite number with 24 divisors. Its prime factorisation is 3 × × 11 × 13. Divisors (24): 1, 3, 7, 11, 13, 21, 33, 39, 49, 77, 91, 143, 147, 231, 273, 429 … 21021.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21021: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21021 is composite. Its prime factorisation is
- 3
The divisors add up to 38304; without 21021 itself that is 17283, so 21021 is deficient (17283 is less than 21021). Euler's totient φ(21021) = 10080 numbers up to 21021 share no factor with it.
- 4
The digits of 21021 add up to 6, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 87 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21021 = 3 \times 7^{2} \times 11 \times 13 \]21021 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 38304 |
| Euler totient φ(n) | 10080 |
| Square | 441882441 |
| Cube | 9288810792261 |
| Square root | 144.986206 (= 7√429) |
| Digit sum / digital root | 6 / 6 |
| Collatz steps to 1 | 87 |
| Scientific notation | 2.1021 × |
21021 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and twenty-one |
| Binary (base 2) | 101001000011101 |
| Octal (base 8) | 51035 |
| Hexadecimal (base 16) | 521D |
| Base 3 | 1001211120 |
| As time | 21021 seconds = 5 h 50 min 21 s |
Is 21021 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | No (remainder 1) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21021 ÷ 3 = 7007) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 1) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (21021 ÷ 7 = 3003) | A number is divisible by 7 if double the last digit and subtract it from the rest: the result is a multiple of 7. |
| 8 | No (remainder 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | Yes (21021 ÷ 11 = 1911) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21021 a prime number?
No. 21021 = 3 × × 11 × 13, so it is divisible by 3.
What are the factors of 21021?
1, 3, 7, 11, 13, 21, 33, 39, 49, 77, 91, 143, 147, 231, 273, 429, 539, 637, 1001, 1617, 1911, 3003, 7007, 21021.
What is 21021 in binary?
101001000011101 (hexadecimal 521D, octal 51035).
What is the square root of 21021?
About 144.9862, exactly 7√429.
Is 21021 divisible by 3?
Yes. Its digits add up to 6, a multiple of 3.
What is special about the number 21021?
21021 is a happy number: repeatedly adding the squares of its digits reaches 1.